Host Galaxy 3 – Messier 31 (21 XGOs)
Photo: Andromeda Galaxy (Messiers 31, 32, and 110), taken on October 5, 2013 at the Deerlick Astronomy Village near Sharon, Georgia during the 2013 Peach State Star Gaze. Explore Scientific ED 102, Canon T 1i, 199 x 15 Seconds, unguided, processed in Pixinsight.
There are several hundred globular clusters in Messier 31, the Andromeda Galaxy. An early catalog, which used the designation “G” for each cluster, was by Wallace L. W. Sargent, Charles T. Kowal, F. D. A. Hartwick, and Sidney van den Bergh. It was titled “Search for globular clusters in M31. I – The disk and the minor axis” and was published in The Astronomical Journal, Vol. 82, pp. 947–953 (December 1977). The catalog is sometimes referred to by its authors’ last initials, or the SKBH catalog.
This catalog was later expanded and revised several times. The basis of these more recent catalogs was an article entitled “A search for globular clusters in M31” by P. Battistini, F. Bonoli, A. Braccesi, F. Fusi Pecci, B. Marano, and A. Vignato in Astronomy and Astrophysics Supplement Series, Vol. 42, pp. 357–369 (1980).
Today, it is likely that while searching for globs in Messier 31 one finds the designation for the latest version of the catalog, which is known as the Revised Bologna Catalogue. It uses the designation “Bol” for each globular cluster.
This history presents a bit of a challenge for this XGO project, in that sometimes I encountered “G” designations, and other times “Bol” designations. For instance, in Sky Safari (which I tend to use) globs are identified with “Bol.” But in other sources, the “G” is used.
Here is how I annotated my photo. I loaded the photo into PixInsight and then used an open-source script from Seti Astro called “What’s in my image.” You can have the script annotate only one type of object; I chose globs. It plots all the globs it has in its catalog onto the photo. However, some of the catalog entries are do not appear in my photo (they are too small or may SNR is too low to catch them.). Fortunately, the script has a clever feature that allows you to have it annotate only the catalog entries that it finds in your photo, so I used that.
My photo was taken in October of 2013, so I turned the date in Sky Safari back to that day and time. I also oriented my photo to match, as closely as possible, the way it was shown in Sky Safari. I then had Sky Safari indicate the globs in Messier 31; they came up as Bol designations. I star hopped on my unannotated photo, locating the globs Sky Safari found, and annotated them. However, instead of using the Bol designations, I converted them to the G designations. I used Google Gemini to do this. Here is a chart showing how the Bol and G designations correspond (at least according to Gemini!):
